It will not apply to unaccompanied minors, a justice department official told US media on Friday.

Under US law, there is a legal obligation to hear asylum claims from migrants if they say they fear violence in their home countries.

Under international law, those who do have a serious fear of persecution are considered refugees.

Until now asylum seekers have been entitled to a hearing in the US regardless of how they arrived in the country.

Mr Trump invoked the same executive power he used to justify his travel ban on people from several Muslim-majority nations last year. The plan is expected to be quickly challenged in court.

What have critics said?

The American Civil Liberties Union (ACLU), a group that defends individual rights, declared the move "illegal". Along with the Southern Poverty Law Center and the Center for Constitutional Rights, it filed a lawsuit to block the order in a federal courthouse in San Francisco on Friday.

"US law specifically allows individuals to apply for asylum whether or not they are at a port of entry," the ACLU said in a statement.